1. Field of the Invention
The invention relates to a novel type of multibranch osteosynthesis clip having dynamic-compression, self-retention and mechanical stability properties.
2. Discussion of the Related Art
The term "dynamic compression" signifies the ability of certain clips to generate a resultant compressive force between the points at which they are implanted and, more particularly, on either side of a bone fracture focus.
Surgical clips used for reduction of fractures and fixation of bones and soft tissue must have several essential properties. First, they must develop a compression effect which is constant over time. They must be well anchored so as to prevent them from detaching after implantation, which detachment is generally inherent with the movements of the joint or simply of the bone on which they are implanted. In addition, the stabilization of the fracture zone by good immobilization constitutes an important condition for achieving bone consolidation. Finally, the mode of implantation or removal of the clips must be simple, easy to employ and generate a minimum of bone traumatism.
Among the various types of clips hitherto known, there is one in which said clips are made of a martensitic material, for example an alloy of the nickel/titanium titanium/niobium type, and which are given a so-called shape-memory phenomenon capable of causing movement of their ends together when the clip is at a temperature greater than the austenitic transformation temperature of the material which forms it. This shape-memory phenomenon is due to reversible thermoelastic martensitic transformation. This phenomenon, which is now well known, consists in giving a defined shape to a material which is treated at a temperature greater than the austenitic transformation temperature A.sub.s of the material, then in giving it another shape, which is also defined, at a temperature less than the martensitic temperature M.sub.s of the material, and repeating this operation a certain number of times, depending on the nature of the alloy used, in order to give this material its final shape memory. The martensitic temperature is less than the austenitic temperature.
Although these clips indeed make it possible to generate dynamic compression at the end of their branches, this generally proves insufficient for the complete fracture at which they are implanted, and even sometimes detrimental, since this compression is asymmetric. In fact, it has a tendency to draw together the deep part of the zone of the fracture and move apart the surface part of this same zone.
In order to overcome these drawbacks, an osteosynthesis clip was proposed in document EP-A-0,488,906 of the Applicant, made of martensitic material in which the change in temperature from the martensitic temperature the austenitic temperature induces shortening of the length of the base of the clip, at least partially, and, in conjunction, drawing together of the ends of said constituent branches of the clip. In addition to the generation by this type of clip of a dynamic compression which is constant over time and homogeneous, it also allows compression both at the surface part of the bone and in its deep part, in view of the fact that the ends of the branches which constitute it are also educated to move toward each other.
However, all double-branch clips do not give mechanical stability to the focus of the bone fracture. In fact, it is often necessary to position several clips in order to achieve this stability, requiring several consecutive operations and also leading to imperfect stability.
In addition, this type of clip is difficult to produce, in view of its particular shape, especially of the arrangement at its base of a portion with reduced cross section which therefore leads to an education which is difficult to induce.